1. Field of the Invention
This invention relates generally to wheel cover retention systems and more particularly to a grip ring system having non-scratch wheel rim engagement.
2. Background History
The implementation of metal grip rings for mounting plastic wheel covers in automotive applications was exemplified in U.S. Pat. No. 3,876,257 issued to the assignee of the present invention. Disclosed in such patent was a plastic wheel cover having an annular channel on its inner face. Seated in the channel was a metal grip ring having a plurality of axially extending legs with the distal portion of each leg being radially outwardly bent to form sharp edged wheel rim engaging tooth. The edges of each tooth, and especially the corners thereof, were configured with sharp relatively hard points to retain the wheel cover in position.
In order to accommodate dimensional variations in the axial depth of the wheel rim within tolerance limits, every other leg was shorter in length than the adjacent leg. The teeth of the short legs preferably engaged the wheel rim axially short of a hollow draw bead step and the teeth of the long legs preferably engaged the draw bead step.
While such grip ring structure gained widespread acceptance, the retention system suffered from certain disadvantages. The sharp edged teeth often scratched paint from the surface of the wheel rim, exposing the steel rim to moisture and road salts which resulted in accelerated corrosion of the exposed wheel rim surfaces.
Further, since the axial depth the legs projected into the wheel rim was fixed by the seating of the grip ring at the bottom of the wheel cover channel, the retention system did not readily accommodate the wide axial tolerance permitted in wheel rims. In some instances, where the axial depth of the draw bead step varied, the teeth of the long legs did not engage the draw bead step. In other instances, within tolerance dimensional wheel rim diameter variations resulted in radially inward deflection of the short legs such that the grip ring distorted to the extent that the long legs did not contact the wheel rim.
In addition, when wheels with mounted wheel covers were subjected to tramp testing in simulation of repeated pot hole engagement, for determining whether extreme driving conditions would dislodge a wheel cover, internal stresses on the wheel cover grip ring channel walls resulted in stress cracks and fractures in the plastic wheel cover, particularly in spoke or bridge areas which separated vent openings.
Rather than utilize thicker or reenforced plastic wheel covers to withstand the internal stresses, it occurred to Applicant that if the length of each leg of a grip ring could be adjustably fixed to conform to the particular axial depth dimensions of a wheel rim, one would be assured that the length of each leg was appropriate to assure proper seating in a wheel rim draw bead step. It further occurred to Applicant that internal stresses may be reduced without significant loss of retentive strength by providing fewer legs which would engage only the draw bead step and by altering the nature of the engagement between the grip ring legs and the wheel rim draw bead step.